1. Field of the Invention
The invention relates in general to a method of patterning a dummy layer, and more particularly to a method of patterning a dummy layer by considering a dark/clear ratio.
2. Description of the Related Art
In the semiconductor IC process, after forming a shallow trench isolation (STI), there are active regions and inactive regions (dummy pattern regions) defined by the shallow trench isolation on a substrate. There are lots of devices including MOS devices or memory cells formed in the active region on the substrate. Metal interconnects are then formed on these devices for connecting the active regions. The metal interconnects usually elongate over the active regions. In the inactive regions there are no devices. The dummy pattern layer is formed in the inactive regions and is used to increase the performance of chemical mechanical polishing (CMP) on active regions and inactive regions. That is, the function of the dummy layer is to make the polishing rate on active regions the same as the polishing rate on inactive regions. Usually, the conventional dummy pattern layer contains random distributed patterns.
Conventionally, the method of forming a dummy pattern layer is very rough. First, an area of devices and an area of relevant devices are defined. The area of devices and the area of relevant devices are sized (a computer command) by magnifying them to form sizing regions. Next, the sizing regions are united to form a non-dummy pattern region. A dummy pattern region is defined as all regions on the substrate excluding the non-dummy pattern region. Then a dummy layer is formed in the dummy pattern region.
In the integrated circuits (IC) process, the conventional method of patterning a dummy layer includes lots of drawbacks. For example, when patterning the dummy layer, the conventional method of patterning a dummy layer doesn't take the dark/clear ratio into consideration. If the dark/clear ratio of the sizing regions is very different from the dark/clear ratio of the dummy layers, the polishing rate on the sizing regions is also very different from the polishing rate on the dummy pattern region. Therefore, there are residues such as silicon nitride formed in the dummy pattern region which cause a loading effect. The loading effect decreases the performance of chemical mechanical polishing.